It was narrated that Abu Dharr said:
"I said: 'O Messenger of Allah (ﷺ), which slave is best?' He said: 'The one who is most precious to his master and most valuable in price.' " (FR)
English reference (FR): Vol. 3, Book 19, Hadith 2523 (FR)
Arabic reference (FR): Book 19, Hadith 2619 (FR)